1. Field of the Invention
The present invention relates to a binder resin composition for a magnetic recording medium and to a method of manufacturing the same. More particularly, the present invention relates to a binder resin composition for a magnetic recording medium, that permits the formation of a coating with suitable flexibility as a layer contained in a magnetic recording medium, and to a method of manufacturing the same.
Still further, the present invention relates to a magnetic recording medium having a radiation-cured layer formed using the above composition.
2. Discussion of the Background
In particulate magnetic recording media, binders play important roles in the dispersibility of magnetic and nonmagnetic powders, coating durability, electromagnetic characteristics, running durability, and the like. Accordingly, various research has been conducted on binders for magnetic recording media.
Conventionally, thermosetting resins and thermoplastic resins such as vinyl chloride resins, polyurethane resins, polyester resins, and acrylic resins have been widely employed as binders in magnetic recording media. In contrast, in recent years, the use of radiation-curable resins incorporating radiation-curable functional groups as binders for magnetic recording media has been proposed to obtain tougher coatings with good productivity. In this regard, reference can be made to, for example, Japanese Unexamined Patent Publication (KOKAI) No. 2005-182985 or English language family member US2005/118459A1 and U.S. Pat. No. 7,201,978, Japanese Unexamined Patent Publication (KOKAI) No. 2004-352804 or English language family member US2004/0241497A1 and U.S. Pat. No. 7,001,955, Japanese Unexamined Patent Publication (KOKAI) No. 2005-8866 or English language family member US2004/241453A1, and Japanese Patent No. 3,125,947, which are expressly incorporated herein by reference in their entirety.
Vinyl chloride resins are known to form tough coatings. As described in the above publications, the incorporation of a radiation-curable functional group makes it possible to form a further tough coating. However, to obtain a magnetic recording medium having good running durability, it is not enough to form a high-strength coating in a magnetic recording medium. Coatings that are strong but lack flexibility are brittle and tend to break. Thus, with repeated running, there may be a risk that a portion of the film will be damaged and drop out, or cause the generation of matter that adheres to the head. In conventional radiation-curable vinyl chloride resins such as those described in the above publications, cured films formed by subjecting compositions containing such resins to a radiation curing treatment are tough but lack flexibility. Thus, there is need for further improvement in the binder resins employed in magnetic recording media.